Cryptosporidium kills AIDS victims in Dallas. Who will the pathogen claim next?

"If you don't look for it, you don't find it," Tulu says.
In fact, the tests required to find crypto in a stool sample are extremely specialized. Some experts think definitive testing requires a biopsy. In the absence of a major education program, there is little inclination on the part of doctors to seek such tests every time a patient has a bout of extreme diarrhea.

"We have only had five [non-fatal] cases of cryptosporidiosis reported in the last year," Tulu says. "We don't know if there is a greater magnitude, because our reporting system isn't strong."

Two of the cases known to Don Maison of AIDS Services were fatal. But Tulu says he had no data at all showing cryptosporidiosis associated with deaths in Dallas County. He conceded that there may be many cases not captured by his data-gathering system.

"There may be a lot that people don't tell us about," he says.
Tulu dismisses crypto as "not a very serious problem," but it's an eerily casual analysis, given the response of many other communities and governments around the world.

Last month the British government ordered its water industry to spend between $12 and $16 million a year on new filtering technology and testing to take crypto out of drinking water. The new rules require water companies to test their product for crypto "continuously" rather than every 24 hours.

Stewart says proudly that the Dallas agency tests for crypto once a month.
Daniel Okun, a professor at the University of North Carolina at Chapel Hill who is considered one of the world's top authorities on testing for crypto, says monthly tests would be "not at all adequate or useful" for a system such as Dallas'--a groundwater and reservoir system subject to sudden runoff and muddiness.

Stewart concedes that there is crypto in the "raw" water that comes into the Dallas system, but by the time this story went to press, he still had not shown the Dallas Observer any test data for raw water. Okun said these numbers would be "essential" to knowing whether Dallas' drinking water is at risk.

The membrane filters capable of eradicating crypto from water are based on bundles of tiny straws gathered in long silver tubes. Water is forced into the skin of the straws through holes far too small to allow microbes like crypto or giardia lamblia to pass.

Milwaukee installed the new membrane micron filters after its 1993 outbreak. Since then, some mid-sized cities have followed suit, including Marquette, Michigan; and Kenosha, Wisconsin.

New York City, which has never filtered its drinking water at all, relying instead on "pristine" sources for its water, promised in federal court last May to build a $1 billion filtration plant. Experts and public-health advocates are pushing hard to ensure that the level of filtration at the new plant will go up to and include the membrane technology needed to eradicate crypto from drinking water.

Until the EPA brought suit against it, New York had been among a select sorority of cities--including Seattle, Portland, San Francisco, and Boston--that owned or controlled all of their own reservoirs and the land around them. These cities typically fenced the land around the reservoirs and guaranteed the purity of the run-off. Because their source water was considered pure, they were allowed to use it unfiltered.

But the EPA convinced a federal judge this year that New York's Croton watershed in Westchester and Putnam Counties is no longer pristine, fenced or not, and that the city needs to filter all of its water to protect the public health.

One of the concerns about the Dallas water system is that it draws drinking water from unprotected reservoirs in North and East Texas. In response to a question about source water for the city, Stewart said at first that all of the reservoirs serving the city were protected and included a "buffer zone of like 1,000 feet or 2,000 feet or something where you can't come in and do anything close to the lake."

When I suggested that I had personally fished on several of those lakes and that the lakes seemed to be surrounded by houses and cows, Stewart said, "Well, subdivisions within that buffer are not your problem, even where you have septic tanks, if they are monitored, and cows are only a problem where you have large feedlots."

The bottom line is that Dallas has an unprotected water source--considered by experts to be extremely dangerous, because dirty run-off tends to front-load the water-treatment system with way more crypto, giardia, and other disease than it can possibly filter.

The filtration system used in the three main plants that provide water to Dallas does not include membrane-filter technology--the only method known to remove crypto entirely from the water.

The Elm Fork Plant does include a system that uses ozone, in addition to chlorine, to enhance disinfection. According to the Centers for Disease Control, ozone appears to be effective against crypto and does not produce the same harmful by-products as chlorine.

But on any given day, as little as a third of the city's drinking water may come from the Elm Fork plant. And while scientists have not yet determined how many oocysts it takes to launch an infection of a human being, the number appears to be quite small. Minuscule traces in the water, in other words, may be enough to severely sicken the unlucky people who drink at the wrong moment.